1. Field of the Invention
The present invention relates to a system of agitation of the acid in a large lead-sulfuric acid storage battery. More specifically, the present invention relates to a system and method of agitating the acid in large lead-sulfuric acid batteries of the calcium type through the use of an air-lift.
2. Description of the Related Art
In large lead-sulfuric acid batteries of the calcium type, during a charging operation, lead sulfate on both electrodes is converted to sulfuric acid as the positive electrode is converted to PbO.sub.2 and the negative electrode is converted from lead sulfate to metallic lead. The solution of sulfuric acid which forms as a film at the electrode-electrolyte interface is more concentrated than the ambient acid and tends to sink to the bottom of the cell because it is more dense. Conversely, during discharge operations, the reverse takes place. The sulfate radical leaves the solution to react with each electrode, and the concentration of the sulfuric acid in the film by the electrode becomes less concentrated than the ambient acid and tends to rise to the top because it is less dense. If this segregation of acid were permitted to continue, the capacity of the battery to deliver power would be reduced and the battery cell could be ruined. To restore the sulfuric acid to a uniform concentration, each cell is provided with air lifts which operate continuously and raise the acid from the bottom to the top. An air lift consists of a pair of tubes of special design. The inner tube descends down into the acid; the outer tube of larger dimensions surrounds the inner tube and extends almost to the bottom of the acid. The outer tube has a side opening just above the level of the acid. When air is sparged from the inner tube into the acid, bubbles rise within the outer tube and lift acid from the bottom of the cell to the outlet of the outer tube where it is discharged back into the acid at the top of the cell. Thus, the acid is continually mixed to obtain a uniform concentration from bottom to top.
The sparger tube at the bottom of the air lift slowly becomes plugged with a precipitate of calcium sulfate and has to be cleaned or replaced. The necessary periodic inspection and replacement of sparger tubes requires a considerable effort.